Nyasa Raymond B, Kimbi Helen K, Zofou Denis, DeBarry Jeremy D, Kissinger Jessica C, Titanji Vincent P K
Biotechnology Unit, Faculty of Science, University of Buea, Buea, Cameroon.
Department of Medical Laboratory Sciences, Faculty of Health Sciences, University of Bamenda, Bamenda, NWR, Cameroon.
Malar J. 2016 May 20;15(1):281. doi: 10.1186/s12936-016-1337-z.
The search for a vaccine against malaria caused by Plasmodium falciparum has lasted for more than 100 years, with considerable progress in the identification of a number of vaccine candidates. The post-genomic era offers new opportunities for an expedited search using rational vaccine design and prioritization of key B-cell epitopes involved in natural acquired immunity.
Malaria vaccine candidate genes that have reached clinical trial were searched on an evolutionary relationship tree, to determine their level of lineage-specificity. Ten other genes with similar protein features and level of lineage specificity to the vaccine candidates were randomly selected, and computationally evaluated for the presence of B-cell epitopes. The protein fragment with maximum probability of putative epitopes were synthesized and used in an ELISA experiment to determine the presence of antibodies to these peptides, in the serum of malaria patients and healthy malaria uninfected inhabitants from a malaria endemic region (Bolifamba), alongside with a vaccine candidate EBA-175.
Two peptide fragments of 25 and 30 amino acid length from PF3D7_1233400 and PF3D7_1437500 respectively, coded as PF4-123 and PF4-143 were shown to contain B-cell epitope(s). Total IgG antibodies to these peptides were not significantly different between sick and healthy participants, but cytophilic antibodies to these peptides were significantly higher in healthy participants (p < 0.03). Total IgG to the vaccine candidate EBA-175 was significantly higher in sick participants than in healthy participants, likewise cytophilic antibodies (p < 0.04). Antibodies to the peptides PF4-123 and PF4-143 correlated negatively (p = 0.025 and 0.008 and r = -0.291 and -0.345, respectively) to parasite load. Total IgG antibodies to EBA-175 showed a negative correlation to parasite load (r = -0.144), which was not significant (p = 0.276). Duration of stay in Bolifamba also negatively correlated with parasite load (p = 0.026, r = -0.419) and total IgG to PF4-143 was significantly associated with prolonged duration of stay in the locality of Bolifamba, Cameroon (p = 0.006, r = 0.361).
The present study has identified two genes PF3D7_1233400 and PF3D7_1437500 containing peptide fragment (PF4-123 and PF4-143) with B-cell epitopes that are correlated with naturally acquired immunity to malaria. A pipeline has been developed for rapid identification of other B-cell epitopes involved in naturally acquired immunity.
寻找针对恶性疟原虫引起的疟疾的疫苗已持续了100多年，在确定多种候选疫苗方面取得了相当大的进展。后基因组时代为利用合理的疫苗设计和对自然获得性免疫中关键B细胞表位进行优先排序来加速搜索提供了新机会。
在进化关系树上搜索已进入临床试验的疟疾候选疫苗基因，以确定其谱系特异性水平。随机选择另外10个与候选疫苗具有相似蛋白质特征和谱系特异性水平的基因，并通过计算评估B细胞表位的存在情况。合成具有推定表位最大可能性的蛋白质片段，并用于酶联免疫吸附测定（ELISA）实验，以确定疟疾流行地区（博利凡巴）疟疾患者和未感染疟疾的健康居民血清中针对这些肽的抗体的存在情况，同时以候选疫苗EBA - 175作为对照。
分别来自PF3D7_1233400和PF3D7_1437500的两个长度为25和30个氨基酸的肽片段，编码为PF4 - 123和PF4 - 143，被证明含有B细胞表位。患病参与者和健康参与者之间针对这些肽的总IgG抗体没有显著差异，但健康参与者中针对这些肽的嗜细胞抗体显著更高（p < 0.03）。患病参与者中针对候选疫苗EBA - 175的总IgG显著高于健康参与者，嗜细胞抗体也是如此（p < 0.04）。针对肽PF4 - 123和PF4 - 143的抗体与寄生虫载量呈负相关（p分别为0.025和0.008，r分别为 - 0.291和 - 0.345）。针对EBA - 175的总IgG抗体与寄生虫载量呈负相关（r = - 0.144），但不显著（p = 0.276）。在博利凡巴的停留时间也与寄生虫载量呈负相关（p = 0.026，r = - 0.419），并且针对PF4 - 143的总IgG与在喀麦隆博利凡巴地区的停留时间延长显著相关（p = 0.006，r = 0.361）。
本研究鉴定出两个基因PF3D7_1233400和PF3D7_1437500，其包含的肽片段（PF4 - 123和PF4 - 143）具有与疟疾自然获得性免疫相关的B细胞表位。已开发出一种流程用于快速鉴定参与自然获得性免疫的其他B细胞表位。
